The present invention relates to a near-field measurement system and a near-field measurement method and, more particularly, to a near-field measurement system and a near-field measurement method of measuring an electric field intensity distribution of an antenna in a near field region.
In recent years, in wireless communication such as mobile communication, modulated waves in a high frequency band of several GHz or more and a broadband of tens of MHz or more are used as a radio signal. Further, a transmission device that transmits a radio signal in a broader band, which corresponds to IEEE 802.11ad, 5G cellular, or the like in which a signal in a broader band that is a millimeter wave band is used, is needed in the future. Further, a demand for analysis of directivity of an antenna mounted on such a transmission device is assumed.
A near-field measurement system 200 that includes an antenna under measurement 220, a transmission device 210 that supplies a high frequency transmission signal to the antenna under measurement 220, a measurement antenna 51 that receives radio waves from the antenna under measurement 220 near the antenna under measurement 220, down-converters 53a and 53b, A/D converters 54a and 54b, and a calculation unit 55, and scans the measurement antenna 51 and measures a near field in a two-dimensional plane facing the antenna under measurement 220 as illustrated in FIG. 17 has been conventionally proposed as a device for measuring, in a near field region, an electric field intensity distribution of an antenna in order to calculate directivity of the antenna (for example, see Patent Document 1).
The calculation unit 55 in the near-field measurement system 200 extracts phase information from a received signal of the measurement antenna 51. Further, the calculation unit 55 can measure amplitude of an electric field generated by the antenna under measurement 220 simultaneously with a phase thereof.
In the near-field measurement system 200 of the related art, a transmission signal output from the transmission device 210 is divided in front of the antenna under measurement 220 and input to the calculation unit 55 in the device via a down-converter 53b and an A/D converter 54b in order to obtain a reference of a phase. In such a configuration, it is necessary for the down-converter 53a for the measurement antenna 51 and the down-converter 53b for phase reference to be arranged in the device.